In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Cermets tools are used with good results in finishing operations of steel but, due to their brittleness, cermets tools are not used in high productivity machining operations together with large cutting depths and large feeds requiring increased toughness. In addition, cermets tools are not used in machining of cast irons, especially not in medium to roughing operations.
The various cast iron grades are machined with use of chemical vapor deposition (CVD) coated cemented carbide cutting tool inserts. Grey cast iron is also machined with silicon nitride based ceramic cutting tools. However ceramic tools are expensive because of the high manufacturing cost. It is therefore a desire, if possible, to replace ceramic tools with less expensive tools. The ceramic tools, such as based on silicon nitride, perform well in grey cast iron, however, show limited tool life in nodular cast iron. Thus, conventional coated cemented carbide tools are used in nodular cast iron area.
However, there are demands from various machining industries for tools with higher productivity and longer tool life than that obtained by conventional coated cemented carbide.
Cemented carbide cutting tools coated with various types of hard CVD layers have been commercially available for years. Such tool coatings are generally built up by one Ti(C,N) and one Al2O3 hard layer where the Ti(C,N) is the innermost layer adjacent to the cemented carbide. The thickness of the individual layers is carefully chosen to suit different cutting applications and work-piece materials, e.g., cast iron and various steel grades. Coated cemented carbide tool inserts may be used for both continuous and interrupted cutting operations of various types of steels and cast irons.
U.S. Pat. No. 6,007,909, discloses coated cutting tools comprising CVD 1-20 μm thick coating on a Ti based carbonitride cermet body, used in steel cutting, such as finishing operations with relatively small cutting depths. The coating should have compressive residual stresses of 100-800 MPa.
U.S. Pat. No. 6,183,846 disclose a coated cutting tool including a hard coating on a surface of a base material of cemented carbide or cermet. The hard coating includes an inner layer on the base material, an intermediate layer on the inner layer and an outer layer on the intermediate layer. The inner layer with a thickness of 0.1 to 5 μm consists of a carbide, a nitride, a carbonitride, a carbooxide, a carboxinitride or a boronitride of Ti. The intermediate layer consists of Al2O3 with a thickness of 5 to 50 μm or ZrO2 with a thickness of 0.5 to 20 μm. The outer layer with a thickness of 5 to 100 μm consists of a carbide, a nitride, a carbonitride, a carbo-oxide, a carboxinitride or a boronitride of Ti.
EP 1643012A discloses a method for high speed machining of a metallic work piece at a cutting speed of 800-1500 m/min, a cutting depth of 2-4 mm, and a feed rate of 0.3-0.7 mm/rev with a coated cemented carbide cutting tool. The cutting tool comprises a coating as a monolayer or multiple layers with a total thickness of 25-75 μm and a cemented carbide body with hardness of >1600 HV3, preferably over 1700 HV3. The best results are obtained in machining of grey cast iron.